Formation of hollow Ag/Au nanostructures in seeding approach: The competition of hydroxyl groups with chloride ions to Ag+

Formation of hollow Ag/Au nanostructures by using 30 nm silver nanoparticles as seeds and the mixtures of HAuCl4 and hydroxylamine as the growth solutions under pH 5.5 and 11.0 was investigated systematically and quantitatively. The hollow Ag/Au nanostructures prepared under pH 11.0 were flower-like in shape while those prepared under pH 5.5 were irregular in shape. It was identified that pH of the reaction system had little effect on the galvanic replacement process (the reduction of Au3+ by Ag seeds). Formation of the hollow Ag/Au nanostructures was primarily dominated by the competition of hydroxyl groups with chloride ions to the Ag+ ions released from the galvanic reaction. At pH 5.5, the resulting hollow Ag/Au nanostructures tended to be irregular in shape due to the presence of AgCl on the seed surface which was difficult to be reduced and thus the deposition of gold was suppressed. At pH 11.0, the resulting hollow Ag/Au nanostructures were flower-like in shape due to the facilitated deposition of the gold upon the dissolution of AgCl. The morphologies and optical properties of the hollow Ag/Au nanostructures were tunable by changing pH and/or concentration of Cl− ions of the growth solutions.